Dendritic cells (DC) specialize in the uptake of antigen and their presentation to T cells. DC thus play a critical role in antigen-specific immune responses.
DC are represented by a diverse population of morphologically similar cell types distributed widely throughout the body in a variety of lymphoid and non-lymphoid tissues (Caux, et al.,1995, Immunology Today 16:2; Steinman, 1991, Ann. Rev. Immunol. 9:271–296). These cells include lymphoid DC of the spleen, and lymph nodes, Langerhans cells of the epidermis, and veiled cells in the blood circulation. DC are collectively classified as a group based on their morphology, high levels of surface MHC-class II expression as well as several accessory molecules (B7-1[CD80] and B7-2[CD86]) that mediate T cell binding and costimulation (Inaba, et al., 1990, Intern. Rev. Immunol. 6:197–206; Frendenthal, et al., 1990, Proc. Natl. Acad. Sci. USA 87:7698), and absence of certain other surface markers expressed on T cells, B cells, monocytes, and natural killer cells.
DC are bone marrow-derived and migrate as precursors through blood stream to tissues, where they become resident cells such as Langerhans cells in the epidermis.
In the periphery, following pathogen invasion, immature DC such as fresh Langerhans cells are recruited at the site of inflammation (Kaplan, et al., 1992, J. Exp. Med. 175:1717–1728; McWilliam, et al., 1994, J. Exp. Med. 179:1331–1336) where they capture and process antigens, (Inaba, et al., 1986. J. Exp. Med. 164:605–613; Streilein, et al., 1989, J. Immunol. 143:3925–3933; Romani, et al., 1989., J. Exp. Med. 169:1169–1178; Puré, et al., 1990. J. Exp. Med. 172:1459–1469; Schuler, et al., 1985, J. Exp. Med. 161:526–546).
Antigen-loaded DC then migrate from the peripheral tissue via the lymphatics to the T cell rich area of lymph nodes, where the mature DC are called interdigitating cells (IDC) (Austyn, et al., 1988, J. Exp. Med. 167:646–651; Kupiec-Weglinski, et al., 1988, J. Exp. Med. 167:632–645; Larsen, et al., 1990, J. Exp. Med. 172:1483–1494; Fossum, S. 1988, Scand. J. Immunol. 27:97–105; Macatonia, et al., 1987, J. Exp. Med. 166:1654–1667; Kripke, et al., 1990., J. Immunol. 145:2833–2838). At this site, they present the processed antigens to naive T cells and generate an antigen-specific primary T cell response (Liu, et al., 1993, J. Exp. Med. 177:1299–1307; Sornasse, et al., 1992, J. Exp. Med. 175:15–21; Heufler, et al., 1988, J. Exp. Med. 167:700–705).
During their migration from peripheral tissues to lymphoid organs, DC undergo a maturation process encompassing dramatic changes in phenotype and functions (Larsen, et al., 1990, J. Exp. Med. 172:1483–1494; Streilein, et al., 1990, Immunol. Rev. 117:159–184; De Smedt, et al., 1996, J. Exp. Med. 184:1413–1424). In particular, in contrast to immature DC such as fresh Langerhans cells, which capture and process soluble proteins efficiently and are effective at activating specific memory and effector T cells, mature DC such as IDC of lymphoid organs are poor in antigen capture and processing but markedly efficient in naive T cell priming (Inaba, et al., 1986. J. Exp. Med. 164:605–613; Streilein, et al., 1989, J. Immunol. 143:3925–3933; Romani, et al., 1989, J. Exp. Med. 169:1169–1178; Puré, et al., 1990, J. Exp. Med. 172:1459–1469; Sallusto, et al., 1995, J. Exp. Med. 182:389–400; Cella, et al., 1997, Current Opin. Immunol. 9:10–16).
Signals regulating the traffic pattern of DC are complex and not fully understood.
Signals provided by TNFα and LPS are known to induce in vivo migration of resident DC from the tissues to the draining lymphoid organs (De Smedt, et al., 1996, J. Exp. Med. 184:1413–1424; MacPherson, et al., 1995, J. Immunol. 154:1317–1322; Roake, et al., 1995, J. Exp. Med. 181:2237–2247; Cumberbatch et al., 1992, Immunology. 75:257–263; Cumberbatch, et al., 1995, Immunology. 84:31–35).
Chemokines are small molecular weight proteins that regulate leukocyte migration and activation (Oppenheim, 1993, Adv. Exp. Med. Biol. 351:183–186; Schall, et al., 1994, Curr. Opin. Immunol. 6:865–873; Rollins, 1997, Blood 90:909–928; Baggiolini, et al., 1994, Adv. Immunol. 55:97–179). They are secreted by activated leukocytes themselves, and by stromal cells including endothelial cells and epithelial cells upon inflammatory stimuli (Oppenheim, 1993, Adv. Exp. Med. Biol. 351:183–186; Schall, et al., 1994, Curr. Opin. Immunol. 6:865–873; Rollins, 1997, Blood 90:909–928; Baggiolini, et al., 1994, Adv. Immunol. 55:97–179). Responses to chemokines are mediated by seven transmembrane spanning G-protein-coupled receptors (Rollins, 1997, Blood 90:909–928; Premack, et al., 1996, Nat. Med. 2:1174–1178; Murphy, P. M. 1994, Ann. Rev. Immunol. 12:593–633). Several chemokines such as monocyte chemotactic protein (MCP)-3, MCP-4, macrophage inflammatory protein (MIP)-1α, MIP-1β, RANTES (regulated on activation, normal T cell expressed and secreted), SDF-1, Teck (thymus expressed chemokine) and MDC (macrophage derived chemokine) have been reported to attract DC in vitro (Sozzani, et al., 1995, J. Immunol. 155:3292–3295; Sozzani, et al., 1997, J. Immunol. 159:1993–2000; Xu, et al., 1996, J. Leukoc. Biol. 60:365–371; MacPherson, et al., 1995, J. Immunol. 154:1317–1322; Roake, et al., 1995, J. Exp. Med. 181:2237–2247).
In recent years, investigators have attempted to exploit the activity of DC in the treatment of cancer. In an animal model, as few as 2×105 antigen-pulsed DC will induce immunity when injected into naive mice (Inaba at al., 1990, Intern. Rev. Immunol. 6:197–206). Flamand et al. (Eur. J. Immunol., 1994, 24:605–610) pulsed mouse DC with the idiotype antigen from a B-cell lymphoma and injected them into naive mice. This treatment effectively protected the recipient mice from subsequent tumor challenges and established a state of lasting immunity. Injection of antigen alone, or B cells pulsed with antigen, had no effect, suggesting that it was the unique characteristics of DC that were responsible for the anti-tumor response. It has been postulated that DC are not only capable of inducing anti-tumor immunity, but that they are absolutely essential for this process to occur (Ostrand-Rosenberg, 1994, Current Opinion in Immunol. 6:722–727; Grabbe et al., 1995, Immunol. Today 16:117–120; Huang et al., 1994, Science 264:961–965). Huang and coworkers (Huang et al., 1994, Science 264:961–965) inoculated mice with a B7-1 transfected tumor that was known to produce anti-tumor immunity. They demonstrated that only mice with MHC-compatible APC were capable of rejecting a tumor challenge. Studies in humans have demonstrated a similar role for DC. It has been reported that peptide-specific CTL are readily induced from purified CD8+ T cells using peptide-pulsed DC, but are not elicited when peptide-pulsed monocytes are used (Mehta-Damani et al., 1994, J. Immunology 153:996–1003).
Of significant clinical interest, the histologic infiltration of dendritic cells into primary tumor lesions has been associated with significantly prolonged patient survival and a reduced incidence of metastatic disease in patients with bladder, lung, esophageal, gastric and nasopharygeal carcinoma. In contrast, a comparatively poorer clinical prognosis is observed for patients with lesions that exhibit a sparse infiltration with DC and metastatic lesions are frequently deficient in DC infiltration (Becker, 1993, In Vivo 7:187; Zeid et al., 1993, Pathology 25:338; Furihaton et al., 1992, 61:409; Tsujitani et al., 1990, Cancer 66:2012; Gianni et al., 1991, Pathol. Res. Pract. 187:496; Murphy et al., 1993, J. Inv. Dermatol. 100:3358). A patient with advanced B-cell lymphoma was recently treated with DC pulsed with the patient's own tumor idiotype (Hsu et al., 1996, Nature Medicine 2(1):52). This produced a measurable reduction in the patient's B-cell lymphoma. Treatment of prostate cancer using DC pulsed with PSM antigen has been reported by Murphy et al. (The Prostate 1996 29:371).
Techniques have recently emerged for the in vitro propagation of large numbers of DC from circulating monocytes or from CD34 hematopoietic progenitors in response to granulocyte-macrophage colony stimulating factor (GM-CSF) in combination with either interleukin 4 (IL-4) or tissue necrosis factor α (TNFα) (Sallusto et al., 1994, J. Exp. Med. 179:1109–1118; Romani et al., 1994, J. Exp. Med. 180:83–93: Caux et al., 1992, Nature 360:258). The combination of GM-CSF and IL-4 induces peripheral blood monocytes to differentiate into potent DC (Kiertscher and Roth, 1996, J. Leukocyte Biol. 59:208–281). With the combination of these two cytokines a 100-fold increase in the yield of DC can be achieved from peripheral blood in vitro.
In mice, tumor antigen-loaded in vitro generated DC have been shown, by various groups, to prevent the development of tumors and more importantly to induce the regression of established tumors. A clinical trial has been conducted in which patients with melanoma are being treated with GM-CSF-activated APC pulsed with a peptide from the MAGE-1 tumor antigen (Mehta-Damani, et al., 1994, J. Immunology 153:996–1003). Pre-immunization, tumor-infiltrating lymphocytes from two patients were predominantly CD4+ and lacked specific tumor reactivity. In contrast, after immunization tumor infiltrating lymphocytes from the same patients were predominantly CD8+ and demonstrated MAGE-1 specific anti-tumor cytotoxicity. It thus appears from these studies that DC have a unique and potent capacity to stimulate immune responses.
Dendritic cell therapy thus represents a very promising approach to the treatment of disease, in particular, cancer. There is a continuing need for improved materials and methods that can be used not only to expand and activate antigen presenting dendritic cells, but to facilitate the migration of DC so as to be both therapeutically as well as prophylactically useful.